It has been alleged that in March this year, Mbeki called up surgeons at Donald Gordon Medical Centre in Johannesburg to insist that they approve a liver transplant for Tshabalala-Msimang, DA leader Helen Zille said in a statement.

DA spokesman Mike Waters had written to Mushwana to ask him to investigate the allegations about Mbeki's call.

In the letter, Waters said it was also alleged that doctors were instructed to describe Tshabalala-Msimang's condition as being the result of auto-immune hepatitis rather than its true cause, alcoholism.

"If such a call was made, then there are several concerns relating to rights of the public and other patients with end-stage liver disease," he wrote.

Firstly, Mbeki would have misused his public position to oblige doctors to make a decision that was not necessarily medically appropriate.

Secondly, if other patients on the waiting list at the time were in greater need of an urgent transplant, Mbeki's intervention might have obliged doctors to prioritise political over medical factors.

And it was possible a more deserving patient might have lost his or her life as a result.

Thirdly, if Mbeki insisted doctors not reveal the true cause of Tshabalala-Msimang's condition, this was an abuse of public position to conceal facts highly relevant to her position as national minister of health.

"A history of concealed and untreated alcoholism calls into question her capacity to do her job, and the public has a right to know the truth," Waters wrote.

However, a spokesman for Donald Gordon Medical Centre denied it had instructed staffers to lie about the minister's condition while she was there.

The centre's spokesman, Vernon Kinnear, said staffers were only asked to sign a document reminding them of the hospital's policy on not divulging patient information.

The Congress of SA Trade Unions has also urged Mbeki to investigate the allegations.

Cosatu said it supported Mbeki's call on the Sunday Times to produce evidence for its allegations about the minister.

The Sunday Times reported that Tshabalala-Msimang had allegedly stolen from a hospital in Botswana and had been banned from that country as a result, and that chronic alcoholism had necessitated her liver transplant.

The national working committee of the ANC yesterday condemned the "character assassination" of Tshabalala-Msimang and extended its support to her.

"Anyone who may have evidence that any member of the executive may have acted in dereliction of duty should forward such evidence to the Presidency," it said after meeting in Johannesburg. - Sapa